And picking up the parameter and I have tried using ErrorInfo() on the first line of my error procedure but neither shows any details.

I have generated errors using ExceptionThrow and also x is int = 0/0 but neither shows any details.

am I missing something here? I know the online help says "ErrorInfo must be used immediately after the call to the function that failed. Indeed, the call to a WLanguage function can reinitialize and modify the status report returned by ErrorInfo.", but I should be able to pick this up straight away?